该研究确定了β-氨基丁酸(β-aminobutyric acid,BABA)对采后葡萄果实抗病性的诱导模式,并从山梨醇代谢和转录调控的角度分析了BABA调控果实可溶性糖积累的机理。葡萄果实经穿刺后,分别在伤口处注入10 mmol/L BABA溶液或1.0×105个/mL的Botrytis cinerea孢子悬浮液,或先注入BABA溶液再接种病原菌,果实随后于20 ℃下贮藏5 d,每日取样评估果实病害发生情况并测定果实品质、抗性反应和山梨醇代谢相关分子或生化指标。结果表明,单一BABA处理可在较低水平诱导葡萄果实防卫反应,但经BABA处理的葡萄果实在进行B.cinerea接种后,其PRs(VvNPR1、VvPR1、VvPR2和VvPR5)基因表达丰度以及植保素单体含量显著上升,说明10 mmol/L BABA诱导的葡萄果实抗病性反应仅在果实遭受病原菌侵染时才强烈表达,可被归为敏化(priming)抗性模式。同时,BABA处理可诱导葡萄果实贮藏期间山梨醇代谢酶类(S6PDH、NAD+-SDH、NADP+-SDH和SOX)活性的上升,使果实中山梨醇加速转化为葡萄糖和果糖;同时,VvWRKY40转录因子能结合葡萄果实蔗糖合成相关基因VvSS1/VvSS2/VvSPS3启动子区域的W-box元件以提高此类基因的转录水平和蔗糖合成量。因此,BABA不仅能激活的葡萄果实priming抗性从而有效抑制果实贮藏期间灰霉病的发生,而且可通过调控山梨醇代谢和提高VvWRKY40转录活性的方式促进葡萄果实中可溶性糖的积累,说明BABA诱导的果实priming反应具有提升抗病性和维持基础代谢的平衡特征。
The study was performed to determine the mode of β-aminobutyric acid (BABA)-induced disease resistance and to analyze the mechanism involved in BABA-mediated accumulation of soluble sugar on the basis of sorbitol metabolism and transcriptional regulation in postharvest grapes.The punched wounds in each berry were injected with 10 mmol/L BABA solution, 1.0×105 spores/mL spore suspension of Botrytis cinerea or BABA, followed by pathogenic inoculation.Afterwards, the grapes were stored at 20 ℃ for 5 days.The tissue samples were taken daily for assessment of disease occurrence and measurement of molecular and biochemical parameters involved in quality, resistance response, and sorbitol metabolism.Results showed that treatment of grapes with BABA alone could induce a defensive response at the basal level;however, the transcriptional values of PRs genes (VvNPR1, VvPR1, VvPR2, and VvPR5) and the content of individual phytoalexins in BABA-treated grape berries were significantly enhanced upon inoculation of the berries with B.cinerea, indicating that the resistance induced by 10 mmol/L BABA could be attributed to a priming mechanism in grapes since only the BABA-treated fruit showed an enhanced capacity to augment defence responses upon challenge with the pathogen.On the other hand, BABA treatment promoted the activities of a set of sorbitol metabolism-related enzymes, including S6PDH, NAD+-SDH, NADP+-SDH, and SOX, resulting in the accelerated conversion of sorbitol into glucose and fructose.Meanwhile, VvWRKY40 bound to the W-box motif in the promoter of sucrose-metabolizing enzyme genes and activated their transcription, by which BABA indirectly enhanced sucrose synthesis in grapes.Therefore, BABA elicitation not only activated priming resistance to inhibit gray mold disease in grapes during storage but also promoted the accumulation of soluble sugars through the regulation of sorbitol metabolism and transcriptional activity of VvWRKY40, which suggested that the BABA-triggered priming response could exert a balance between elevated disease resistance and maintenance of primary metabolism.
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